It uses the gyros in the phone so you can swing it back and forth and find the sources of the EM radiation. This is particularly useful if you're curious how much EMF your household appliances put off, or if you're feeling more adventurous and investigating a haunting. Mr.Ghost gives you the option to record the fields and listen to them, as well as a more Lord of the Rings option where the detector glows brighter the more powerful the EM field is.